For members requiring wear resistance, sliding properties, and fracture resistance, such as a cutting tool, an wear-resistant member, and a sliding member, a method for improving wear resistance, sliding properties, and fracture resistance is currently used, in which a coating layer is formed on a surface of a substrate composed of a sintered alloy such as a cemented carbide, cermet, or the like, a high-hardness sintered body such as diamond, cBN (cubic boron nitride), or the like, or ceramics such as alumina, silicon nitride, or the like.
As a method for depositing a coating layer, physical vapor deposition methods such as an arc ion plating method, a sputtering method, and the like are widely used. Among coating layer deposited by the physical vapor deposition methods, nitride layers containing Ti and Al as a main component are actively researched, and improvement for increasing the lives of cutting tools are continuously performed. For example, a coating layer having a (TiNbAl)N composition may be deposited, and a coating layer having a (AlTiNbSi)N(O) composition may be deposited. Both of the coating layers improve the oxidation resistance and wear resistance thereof. Further, a coating layer having a (TiWSi)N composition in order to enhance adhesion to a substrate composed of a cemented carbide or the like may be deposited.
In such a physical vapor deposition method, a method of providing a plurality of types of targets in a chamber and depositing a coating layer while rotating a sample so that the sample is in order brought close to the targets is attempted. This method can form a coating layer including a plurality of laminated layers having different compositions.
On the other hand, for example, a cutting tool may comprise an Al2O3—TiC based ceramic substrate called “black ceramic” and a coating layer formed on a surface of the substrate and including a TiAlN layer or the like. The cutting tool shows good cutting performance for cutting high-hardness materials. In addition, a coating layer containing at least one layer of TiC, TiN, and TiCN may be formed by a physical vapor deposition method on an Al2O3—TiC based ceramic substrate containing 0.1 to 5% by weight of iron group metal. The coating layer may enhance adhesion to the ceramic substrate and improve fracture resistance.
In addition, for example, a cutting tool may be composed of a silicon nitride sintered body containing 0.2% by weight or more of yttria (Y2O3) and 0.2% by weight of magnesia (MgO) in a total of 3.5% by weight or less, and 1.3 to 3.5% by weight of oxygen. Porosity in the sintered body of the cutting tool can be decreased to 0.2% by volume or less.
Further, for example, a cutting tool may comprise a cBN substrate and a coating layer of TiC, TiN, Al2O3, or the like deposited on a surface of the substrate. The cutting tool may improve wear resistance in cutting general steel and cast iron. In addition, a cutting tool may comprise a TiAlN layer formed on a surface of a cBN substrate. The cutting tool has a long life in cutting difficult to machine materials such as hardened steel and the like. Further, a cutting tool may comprise a cBN substrate and a coating layer formed on a surface of the substrate. The coating layer has a Ti/Al ratio of a TiAlSiN composition continuously changed. The cutting tool having the coating layer shows good chipping resistance in high-speed deep cutting.
However, the coating layer with the (TiNbAl)N composition, the coating layer with the (AlTiNbSi)N(O) composition, and the coating layer with the (TiWSi)N composition do not have sufficient fracture resistance, and the cutting tools are desired to have a longer life. Also, the cutting tools described above do not have sufficient cutting performance, and the cutting tools are desired to have a longer life.
In addition, the coating layer including a laminate of a nitride layer and an oxide layer does not have sufficient wear resistance.
Therefore, there is a need for improving wear resistance, fracture resistance, and chipping resistance in a cutting tool.